Process for coal liquefaction and catalyst

ABSTRACT

A method for hydroconversion of coal solids in a solvent by contact with molecular hydrogen and catalyst solids in a reactor. The catalyst solids are catalytically active substances including promoted or unpromoted molybdenum on an alumina support material. The support is characterized by bimodal pore distribution with the average diameter of the smaller pores ranging from about 100-200 angstroms and preferably 120-140 angstroms, and average diameter of the larger pores being in excess of 1,000 angstroms.

CROSS-REFERENCE TO RELATED APPLICATION

Reference is made to copending U.S. patent application entitled "Processfor Upgrading Coal Liquids," Ser. No. 020,208, filed simultaneouslyherewith, now abandoned.

BACKGROUND OF THE INVENTION

The invention relates to catalytic hydroconversion of coal to liquid andgaseous products, and more particularly to a supported catalyst for thisprocess including bimodal pore distribution.

A number of processes have been described in the literature relating tothe hydroconversion of pulverized coal to coal liquid in the presence ofmolecular hydrogen and a catalyst in a catalytic reactor. In oneprocess, coal conversion involves slurrifying solid pulverized coal in asolvent which is directed through a reactor with the hydrogen gas streamunder high pressure and temperature. After conversion, the slurryproduct is collected. One such process, referred to as the H-Coalprocess, by Hydrocarbon Research, Inc., is performed in an ebullatedcatalyst fixed tubular reactor in which the catalyst and coal slurry aresuspended and mixed.

The catalyst employed in the above processes include a variety ofcatalytically active substances deposited on porous support particleshaving large surface area. As set out in the background of U.S. Pat. No.3,635,814, previous investigators have indicated that the pore size fora catalyst is on the order of 50 to 250 angstroms with the most frequentpore size being 60 angstroms. Many of such catalysts are of unimodaldistribution, that is, including only one major distribution peak ofaverage diameters of pore volume. On the other hand, there is a producton the market designated HDS-1442A by American Cyanamid Corporation withbimodal pore distribution having a major peak of smaller pore volumedistribution (below 600 angstroms) and a second major peak pore volumedistribution above 1,000 angstroms.

One problem with coal liquefaction catalysts is that they tend todeactivate during use as by clogging of the pores. This limits theeffective life of the catalyst prior to regeneration.

SUMMARY OF THE INVENTION AND OBJECTS

It is an object of the invention to provide a catalyst suitable for thehydroconversion of coal solids capable of producing a low sulfurpumpable liquid product without excessive consumption of hydrogen.

It is another object of the invention to provide a catalyst of theforegoing type which does not deactivate rapidly under coalhydroconversion conditions.

Further objects and features of the invention will be apparent from thefollowing description taken in conjunction with the appended drawings.

In accordance with the above objects, a catalyst is provided which isparticularly useful for coal liquefaction. It includes a catalyticallyactive substance, preferably unpromoted molybdenum or molybdenumpromoted with cobalt or nickel, supported on particles with bimodal poredistribution. The smaller pore average diameter range from 100-200angstroms and preferably 100-150 angstroms while the large pore averagediameter is in excess of 1000 angstroms. This catalyst promotes highcoal conversion to form a low sulfur product and with low hydrogenconsumption.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a graph of benzene soluble conversion for a cobalt molybdenumcatalyst on alumina comparing the substrates of the present inventionwith those of the prior art.

FIG. 2 is a graph of desulfurization performance as a function of hourson stream for the catalysts of FIG. 1.

FIG. 3 is a comparison of hydrogenation metals in a plot of conversionin weight percent against hours on stream.

FIG. 4 is a plot of the desulfurization performance of variouscatalysts, some of which employ the support substrate of the presentinvention.

FIG. 5 illustrates pore size distribution plotting pore radius versuspore volume for catalyst substrates of the present invention incomparison to one of the prior art.

FIG. 6 is a plot of catalyst rankings in terms of coal conversion anddifferent conditions than those of FIGS. 3 and 4.

FIGS. 7 and 8 are plots of catalyst rankings of conversion anddesulfurization, respectively, against hours on stream.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention is directed to a catalyst suitable forhydroconversion of coal solids to liquid and gaseous products and to theprocess of hydroconversion. The term "coal" includes any form of solidcarbonaceous substance suitable for catalytic hydroconversion, forexample, bituminous, semi-bituminous, sub-bituminous grades of coalincluding lignites, kerogen, peats, semi-anthracite, and the like.Typically, mined coal is pulverized to a size wherein most of the coalsolids are less than 8 mesh (U.S. sieve series) and typically in thesize range of 8 mesh to 325 mesh and typically about 40 mesh.

In a preferred process, the coal is first formed into a slurry beforecontacting with hydrogen and catalyst. A suitable slurry comprises anorganic solvent, preferably derived from the coal liquefaction process.Because of the difficulties involved in pumping high solids contentslurries, a preferred slurry content is generally less than 70 weightpercent coal solids based upon the slurry mixture. Suitableconcentrations are on the order of 20-70 weight % coal solids.

In the reaction zone, the coal solids undergo liquefaction andhydroconversion. The conversion is accomplished in the presence ofmolecular hydrogen and the catalyst of the present invention. There area number of known coal liquefaction and hydroconversion processes whichemploy a hydrogenation catalyst. In some instances, the coal slurry,catalyst and hydrogen are contacted at elevated temperatures andpressures in the reactor. As set out above, in one process, known as theH-Coal process, the pulverized coal slurry and hydrogen is fed to thereactor in which the catalyst is present. The reaction is performedunder ebullated conditions. Or the reaction may be performed in a fixedbed tubular reactor which contains the catalyst solids. Suitableconditions for performing the hydroconversion such as temperature,pressure, flow rates of reactants, charge and the like are well known tothose skilled in the art. One catalytic coal conversion process isdisclosed in U.S. Pat. No. 3,635,814, the disclosure of which isincorporated at this point by reference.

The present invention relates to a catalyst suitable for the performanceof coal liquefaction and hydroconversion as of the foregoing type. Whilethe catalyst will be disclosed in terms of this environment, it shouldbe understood that it has other applications, such as for upgrading coalas disclosed in the aforementioned copending U.S. application entitled"Process for Upgrading Coal Liquids," Ser. No. 020,208, filedsimultaneously herewith, and now abandoned.

A major feature of the present invention is the discovery of anexceptional catalyst for processes of the foregoing type containing aparticular essentially bimodal pore distribution. As defined herein,bimodal distribution means a pore distribution including two major peaksof pore diameters measured as a plot of pore volume in cc/gram versuspore diameter or radius. More specifically, in this bimodaldistribution, the smaller pores are defined as having peakconcentrations being below about 600 angstroms in diameter and thelarger pores are defined as being above that value. The average diameterof the smaller pores range from about 100 to 200 angstroms, andpreferably 100-150 angstroms. The average diameters of the larger poresare in excess of 1,000 angstroms and generally range from 1,000 to10,000 angstroms. A more preferred size distribution for the smallerpore range is about 120 to 140 angstroms average diameter and morespecifically on the order of 125 angstroms. In a preferred product, thesmall pores have diameters predominantly in the range of 70 to 200angstroms.

A number of significant advantages are obtained by use of a substrate ofthe foregoing type for the catalyst. For example, such bimodal catalystsare more active for both coal liquefaction conversion and sulfurreduction. The theory to explain such higher effiency as follows. Thesmaller pores are the most catalytically active. However, small poresare subject to clogging during long term use as during desulfurization.The larger pores may not be catalytically active but provide access tothe smaller pores to account for the ability of the catalyst to convertthe coal to a liquid product at high conversion efficiencies during longterm operation and to provide an ultimate coal liquid of low sulfurcontent and low viscosity.

A suitable surface area for the bimodal substrate particles of thepresent invention is on the order of 100 to 250 m² /gm. This value is afactor in determining the amount of larger pores and smaller pores.

It has been found that at least 5% of larger pores and preferably about7 to 20% of the larger pores are preferable to accomplish the superiorproperties of the present invention. Conversely, it has been found thatthe catalyst preferably includes at least 70% of the smaller pores, andpreferably about 80 to 93%, to provide the desired catalytic activity.

The substrate of the present invention may be formed of conventionalmaterial such as alumina in catalytic form such as gamma-alumina.Although such alumina may be pure, it may contain minor amounts of otheroxides that are inert under the conditions at which it is used. Suitablesubstrate materials, although with different pore size distributions,are set out in Bertolacini et al U.S. Pat. No. 3,393,148, incorporatedherein by reference. Other presently available catalytic substrates mayalso be employed such as those used by Hydrocarbon Research, Inc. in theH-Coal process. These materials are formed from boehmite startingmaterials. The alumina support may contain silica or other materialsinert to the process. Other support materials such as silica-alumina andcatalytically active clays may also be employed.

A variety of procedures may be employed for preparing the aluminasupport particles. In general, the smaller pores are associated with thealumina base material. The larger pores can be formed by knowntechniques such as grinding the alumina into a fine powder and thenbinding the particles together into spheres or extrudates. During thatprocess, the large pores are generated. Other techniques could be toemploy pore growth promotors. Pore growth promotion would beaccomplished by heating the material in the presence of a gas or metalcompound, steaming at elevated temperatures, treating with hydrogen atelevated temperatures, or the like. In another procedure, the largepores may be introduced during preparation of the base material by theuse of a strong mineral or organic acid for leaching. Still anotherprocedure would be to introduce into the alumina structure, a removablematerial which may be volatile or decomposable in the gases by theapplication of heat. For example, ammonium carbonate, naphthalene,anthracene, volatile aromatics, and the like have been employed. Theamount of removable solids employed depends upon the desired pore size.

A number of different catalytically active substances may be depositedon the surface of the bimodal substrate of the present invention. Apreferred catalyst substance is molybdenum in the form of MoO₃. Whenthis material is employed by itself, that is, unpromoted by any othercatalyst, it again provides superior liquefaction performance and slowerconversion declines during time on the stream.

Other known catalysts may be employed as promotors for the molybdenum.For example, nickel and/or cobalt are beneficially employed incombination with the molybdenum for superior desulfurization or othersuperior properties.

A preferred catalyst includes between about 5 and 20 weight % ofmolybdenum measured as MoO₃. If it is employed in combination with theaforementioned promotors, it preferably also includes 0.5 to 4 weight %Co and/or Ni measured as CoO and/or NiO respectively. For example, onepreferred composition includes 3 weight % CoO and 15 weight % MoO₃.

A suitable technique for depositing the catalytic substances on thesubstrate is to impregnate. For example, to deposit molybdenum andcobalt, the catalyst may be impregnated with an aqueous solution ofammonium molybdate and cobalt nitrate. The finished catalysts arecalcined at say 1000° F. and contain a nominal composition of 3 weight %cobalt (CoO) and 15 weight % MoO₃.

The particle size of the catalyst support substrate should be smallenough to provide the desired contact area and to be readily ebullatedas in the H-Coal process. On the other hand, it must be substantiallylarger than the coal particle sizes to be contained in a fixed bed whilethe reactants flow through the same.

A general disclosure of techniques for catalyst formation is found in anarticle by Higginson, G.W., Chem. Eng., Sept. 30, 1974. A more detaileddisclosure of suitable catalyst forming techniques is found in Long etal. U.S. Pat. No. 3,989,645.

A further disclosure of the nature of the present invention is providedby the following specific examples of the practice of the invention. Itshould be understood that the data disclosed serve only as examples andare not intended to limit the scope of the invention.

EXAMPLE 1

A first comparative series of tests were formed comparing the catalystof the present invention with other known catalysts and with the thermallevel. That is, the result obtained by using thermal conversion in theabsence of catalyst. In this series, the catalyst of the presentinvention was prepared as follows. A series of alumina catalysts wasprepared by W. R. Grace Company from boehmite starting material to havepore sizes as illustrated in FIG. 5 and discussed below. The aluminasupport particles were then impregnated with an aqueous solution ofammonium molybdate and cobalt nitrate. The finished catalysts werecalcined at 1000° F. and contained nominally 3% CoO₃ and 15% MoO₃.

Catalysts of the foregoing type were employed with feed stock as setforth in the following Table I.

                  TABLE I                                                         ______________________________________                                         FEEDSTOCK INSPECTIONS                                                        ______________________________________                                                    Hydrotreated Illinois No. 6 Coal                                  Elemental, Wt. %                                                                          Anthracene Oil                                                                             Burning Star Mine                                    ______________________________________                                        Carbon      91.9         67.6                                                 Hydrogen    6.0          4.6                                                  Sulfur      0.4          3.3                                                  Nitrogen    0.6          1.3                                                  Oxygen      1.0          9.0                                                  Moisture    0.03         3.3 -Ash -- 10.9                                     Distillation, °F.                                                      IBP         520                                                               70% Off     677                                                               FBP         847                                                               ______________________________________                                    

The catalyst test conditions are set forth in the following Table II.

                  TABLE II                                                        ______________________________________                                        CATALYST TEST CONDITIONS                                                      ______________________________________                                        Catalyst charge                                                                             :     60 cc, 1/16" extrudate                                    Coal Slurry   :     20 wt. % I11 #6 (-400 mesh)                                                   in hydrogenated anthracene oil                            Reactor Holdup                                                                              :     320 cc                                                    Pressure      :     137 Atm (2000 psi)                                        Temperature   :     427° C. (800° F.)                           H.sub.2 Feed Rate                                                                           :     170 liter/hr (6 SCFH)                                     Slurry Feed Rate                                                                            :     400 g/hr                                                  Residence Time                                                                              :     48 minutes                                                LHSV          :     1.33 g-coal/hr/cc-catalyst                                Mixing Speed  :     1500 rpm                                                  ______________________________________                                    

The catalyst of the present invention, designated the "bimodal catalyst"was compared with a unimodal catalyst having only the smaller pore sizesand not the larger ones. It was also compared with another catalystcontaining nickel instead of cobalt and a third catalyst using thecommercially available HDS-1442A product of American Cyanamid. The poresize of the latter catalyst is compared with the present bimodalcatalyst in FIG. 5.

The coal slurry was pumped into the reactor with hydrogen and catalystand a slurry product stream was removed. Referring to Table 3, theproperties of the HDS-1442A catalyst is compared to two catalysts; onecobalt molybdenum and the other nickel molybdenum on the supportsubstrates of the present invention. The former one is designatedCoMo-G120B and the latter NiMo-G120B. Two different analyticaltechniques, nitrogen desorption and mercury penetration were employed.The abbreviations are as follows:

SA=surface area;

APD=average pore diameter; and

PV=pore volume.

                  TABLE III                                                       ______________________________________                                        CATALYST DATA                                                                        N.sub.2 Desorption                                                                       Hg Penetration                                                        Down           Up         Pore                                                to 20          to 10.sup.5                                                                             Volume                                               angstroms      angstroms of                                                SA   APD    PV     SA   APD  PV   10.sup.3 -10.sup.5 A                        m.sup.2 /g                                                                         A      cc/g   m.sup.2 /g                                                                         A    cc/g % of total                           ______________________________________                                        HDS-1442A                                                                     Fresh    323    58     0.64 344   91  .767 26                                 Spent                                                                         (coke free                                                                    basis    177    65     0.42 120  131  .404 40                                 Regen    191    79     0.55 184  114  .523 27                                 CoMo-G120B                                                                    Fresh    162    111    .615 178  131  .585 17                                 Spent                                                                         (coke free                                                                    basis)   149    92     .419 142  109  .389 22                                 Regen    133    114    .504 149  140  .522 18                                 NiMo-G120B                                                                    Fresh    163    114    200 .624                                                                           180  141  .635 --                                 Spent                       117  147  .433 --                                 Regen    --     --     --   --   --   --   --                                 ______________________________________                                    

A substrate of the present invention was utilized in a series of tests;one utilizing unpromoted molybdenum (designated Mo-G120B) and the otherutilizing the aforementioned CoMo-G120B and compared with HDS-1442Acatalyst in Table IV below.

                  TABLE IV                                                        ______________________________________                                        EVALUATION OF CATALYST PERFORMANCE                                                       HDS-1442A                                                                              Mo-G120B  CoMo-G120B                                      ______________________________________                                        Catalyst Age,                                                                 lbs coal/lbs catalyst                                                                      141        145       138                                         Coal conversion,                                                              wt. % maf    93.7       94.5      94.0                                        Wt. % of dry coal                                                             C.sub.4 -975° F. distillate                                                         41.9       44.8      45.6                                        975° F. + residuum                                                                  26.0       0.44      21.8                                        Sulfur in residual oil,                                                       wt. %        0.46       0.44      0.34                                        975° F. + filter liquid                                                Test period (days on                                                          stream)      10         12        11                                          Viscosity at 450° F.                                                   cps          20,500     7,300     3,800                                       ______________________________________                                    

The product distribution is illustrated under weight % of dry coal withthe C₄ to 975° F. distillate compared against the 975° F. plus residuumsor bottoms. The test period is an indication of the age of the catalyst.

An important feature of the invention is that the distillate of both themolybdenum and cobalt molybdenum catalyst is a higher proportion thanthe residuum, of significant benefit to the invention. In addition, boththe Mo-G120B and CoMo-G120B provided a lower sulfur content in theresidual oil with the latter material providing exceptionally low sulfurcontent.

Referring to FIG. 1, the conversion to benzene soluble products obtainedwith the subject CoMo-G120B catalyst as compared with HDS-1442A. It isapparent that the present product has higher initial activity andmaintains its activity significantly better than the prior art product.Other catalysts are illustrated including a bimodal catalyst with anaverage pore diameter of 200 angstroms (G200B) which is slightly lessactive than catalyst G120B and more active than one using Kaiser averagediameter of 100 angstroms unimodal alumina/(K100U) which exhibited poorperformance.

Another feature of the invention is that the viscosity of the materialis substantially lower for both of the present products in comparison tothe HDS-1442A. Thus, CoMo-G120B has a viscosity of 3800 cps compared to7300 Cps for Mo-G120B and 20,500 cps for the prior art product.

Referring to FIG. 5, the pore size distributions of the CoMo-G120Bsubstrate are compared to that of the prior art HDS-1442A. It isapparent that there is a substantially different bimodal distribution.The prior art product has an average pore diameter substantially belowthat of the present product with a peak pore radius of between 20 andabout 40 angstroms compared to applicant's peak pore radius of about 60to 70 angstroms (120-140 angstroms diameter).

Referring to FIG. 2, desulfurization performance is illustrated. Thesignificantly lower weight % of the sulfur in the product illustratesthe advantage of the present product.

Referring to FIG. 3 and FIG. 4, the effect of varying catalyst metals isillustrated and compared to HDS-1442A using a cobalt molybdenumcatalyst. The activity of the nickel molybdenum product (NiMo-G120B) isintermediate between CoMo-G120B and HDS-1442A with a somewhat higherdeactivation rate indicated for the NiMo catalyst. Addition of silica tothe support or rhenium to the catalyst has no apparent effect. Thenickel promoted or cobalt promoted molybdenum is far superior to thenickel tungsten catalyst. The superior performance of the NiMo-G120Bcatalyst in comparison to HDS-1442A is attributed to the preferredsupport properties of the present substrate.

Referring to FIG. 5, the pore size distribution of fresh and usedCoMo-G120B and HDS-1442A are compared. The bimodal structure of bothcatalysts is evident but the smaller pores in CoMo-G120B are larger thanthe smaller pores in HDS-1442A and, in a preferred pore size rangecenter around a radius of 60-70 angstroms (120-140 angstroms diameter).After use, the HDS-1442A catalyst loses most of its small pore volumewhile the CoMo-G120B retains a substantial part of its small porevolume. Regeneration by controlled burning of coke deposited in thecatalyst restored essentially all of the pore structure of the freshCoMo-G120B.

EXAMPLE 2

A further evaluation of performance was made in the H-Coal continuoustest unit of Example 1 under more severe conditions involving a highercoal solvent concentration (25 weight %) and higher temperature (825°F.). The advantage of CoMo-G120B over HDS-1442A was again clearlydemonstrated as illustrated by the plot of conversion versus time inFIG. 6. The higher hexane soluble conversion obtained with the presentcatalyst is significant because it affects product viscosity, animportant feature with respect to separation of liquid product fromsolid residue and fuel pumpability. As illustrated in FIG. 6, unpromotedmolybdenum yields conversion similar to the cobalt promoted molybdenumproduct. However, the inclusion of cobalt in the catalyst is beneficialto sulfur removal.

EXAMPLE 3

Two cobalt molybdenum on aluminum catalysts, A and B, have an averagepore diameter of about 122 angstroms, but Catalyst A has a bimodal poredistribution with the pores greater than 1000 angstroms in diameteroccupying 10.3% of total pore volume. Catalyst B has a unimodal poredistribution with very few pores beyond 1000 angstroms as illustrated byTable V below.

                  TABLE V                                                         ______________________________________                                        CATALYST INSPECTION DATA                                                              Average                      Pore                                             Pore       Surface   Pore    Volume of                                        Diameter,  Area      Volume  10.sup.3 -10.sup.5 A                     Catalyst                                                                              A          m.sup.2 /g                                                                              cc/g    % of total                               ______________________________________                                        A       122        154       0.60    10.3                                     B       124        160       0.62    2.2                                      ______________________________________                                    

Catalysts A and B, at 60 cc each in a 1/16" extrudable form, were testedfor coal liquification at identical conditions. A 25 weight % ofpowdered Illinois No. 6 Coal slurried in a hydrotreated anthracene oilwas continuously fed along with hydrogen to a continuously stirredreactor under 137 atmospheres and 440° C. Nominal residence time in thereactor was 44 minutes and liquid hourly space velocity (LHSV) based oncoal feed was 1.79 g-coal/hr/cc-catalyst. The results are summarized inTable VI below.

                  TABLE VI                                                        ______________________________________                                        LIQUEFACTION OF ILLINOIS No. 6 COAL                                                     Coal conversion                                                                            Sulfur in                                                        to wt % maf  520° C. +                                                                       Relative                                             Hours on Benzene          residual,                                                                            catalyst                              Catalyst                                                                             stream   solubles 520° C.-                                                                       wt. %  activity                              ______________________________________                                        A       23      80.1     49.4    0.65   57                                           120      71.1     42.0    0.81   15                                    B       23      72.7     41.3    0.74   26                                           120      62.8     36.8    0.93    3                                    ______________________________________                                    

Table VI clearly indicates that the coal conversion to either benzenesoluble liquid or products boiling below 520° C. on a moisture and ashfree basis is much higher for Catalyst A than Catalyst B throughout the120 hour test length. The relative activity is the catalyst activityrelative to its initial activity calculated based on a reaction modelusing benzene soluble conversions. The calculation shows that bothCatalyst A and B have practically the same initial activity for coalliquification owing to the similar average pore diameter, but Catalyst Awith the bimodal pore distribution loses its activity much slower thanCatalyst B. Catalyst A also gave lower sulfur contents in 520° C. plusresidual product or better desulfurization than Catalyst B. This exampleclearly demonstrates the superior performance of the present catalyst.

EXAMPLE 4

Catalyst C, D and E were tested for liquefaction of a subbituminousWyodak coal at the same test conditions as described in Example 3. Theliquefaction solvent was the hydrotreated anthracene oil and coalconcentration was 25 weight %.

Catalysts C and D are respectively molybdenum on alumina and cobaltmolybdenum on aluminum prepared in laboratory by the impregnationmethod, and Catalyst E is a commercial cobalt molybdenum on aluminummanufactured by American Cyanamid Co. Catalyst inspection data are shownin Table VII. Catalyst C and E have bimodal pore distributions butdifferent average pore diameter. Catalyst D has the same average porediameter as Catalyst C, but the pore distribution is unimodal.

                  TABLE VII                                                       ______________________________________                                        CATALYST INSPECTION DATA                                                                      Average         Pore                                          Ca-  Compose-   Pore     Surface                                                                              Vol-  Pore Volume                             tal- tion, wt%  Diameter,                                                                              Area,  ume   of 10.sup.3 -10.sup.5 A,                yst  CoO    MoO.sub.3                                                                             A      m.sup.2 /g                                                                           cc/g  % of total                            ______________________________________                                        C    --     15      123    167    0.65  9.6                                   D    3      16      124    153    0.62  2.2                                   E    3      13       58    323    0.65  26.1                                  ______________________________________                                    

The test results are summarized in Table VIII. Catalyst C, Which isunpromoted molybdenum on 120 angstroms bimodal alumina support, showsnot only the best liquification conversion to benzene soluble materialbut also the lowest sulfur contents of the 520° C. +residual product.

The unimodal catalyst D with 120 angstroms average pore diameter isdefinitely inferior to Catalyst C, but the benzene soluble conversionsare somewhat better than those obtained with Catalyst E having 60angstroms average pore diameter.

For a given liquefaction level, the molybdenum Catalyst C consumes lesshydrogen than cobalt molybdenum Catalyst D or E.

The example points out the importance of average pore diameter around120 angstroms for a higher liquefaction activity, criticality of bimodalpore distribution for maintaining catalyst performance, and a uniqueattribute of molybdenum catalyst for reduced hydrogen usage.

                  TABLE VIII                                                      ______________________________________                                        LIQUEFACTION OF WYODAK COAL                                                                              Sulfur in                                          Ca-  Hours   Coal conversion                                                                             520° C. +                                                                      H.sub.2 consumption                        tal- on      to benzene    residuals,                                                                            wt % of slurry                             yst  stream  solubles, wt % maf                                                                          wt %    feed                                       ______________________________________                                        C    25      80.7          0.19    0.92                                            120     71.8          0.32    0.53                                       D    25      78.3          0.23    1.17                                            120     64.6          0.36    0.52                                       E    20      74.9          0.22    0.94                                            115     63.7          0.36    --                                         ______________________________________                                    

EXAMPLE 5

Short term aging behavior of several CoMo catalysts are discussed andrelated to catalyst surface properties. The short term aging test lastsfor about a week at the fixed standard test conditions and should beregarded as an accelerated deactivation test since the slurry oil usedis relatively heavy and high boiling.

Four catalysts including the reference H-Coal catalyst, HDS-1442A, arelisted in Table IX along with surface properties and apparent bulkdensity. The metals contents are nominally 3% CoO and 15% MoO₃. Averagepore diameter is defined in such a manner that half of the poresmeasured by nitrogen desorption are smaller or greater than thisdiameter. The pore size is used as a primary parameter for correlatingcatalyst performance, since for given pore volume, surface areadecreases with increasing average pore diameter. The pore size rangewhich covers the majority of the pore volumes detectable by nitrogendesorption method gives an indication whether the pores are broadly ornarrowly distributed. The pores greater than 1000 A in diameter, whichare measured by mercury penetration method, are usually created duringthe forming process of a support. These macro pores may not becatalytically active but could serve as feeder pores for transportingmaterials into catalyst interior. Catalysts that contain 1000 A+macropores in more than 10 volume percent of the total mercury pore volumeare regarded as having a bimodal pore size distribution. According tothis classification, only Kaiser-100UP has a unimodal pore distribution;the rest in Table IX have bimodal pore distribution.

                  TABLE IX                                                        ______________________________________                                        COBALT-MOLYBDENA CATALYST                                                     INSPECTION VARYING SURFACE PROPERTIES                                                                             1000A+                                             APD    SA     PV   Major   Pores ABD                                 Catalyst A      m.sup.2 /g                                                                           cc/g Pores A Vol %.sup.(1)                                                                       g/cc                                ______________________________________                                        HDS-1442A                                                                               58    323    .64  20-140 28     0.57                                Kaiser 100UP                                                                           105    195    .70  50-250  4     0.59                                G-120B   111    162    .62  70-200 17     0.68                                G-200B   183     91    .53  105-350                                                                              18     0.73                                ______________________________________                                         .sup.(1) By mercury porosimetry?                                              B = bimodal?                                                                  U = unimodal?                                                                 P = phosphoric acid impregnating aid?                                    

Coal conversion to benzene solubles is plotted versus time on stream inFIG. 7 for four CoMo-alumina catalysts differentiated by average porediameters and pore size distribution. Compared to the referenceHDS-1442A, which has about 60 A average pore diameter, 120 A bimodalcatalyst (G120B) increased the benzene soluble conversion. A furtherincrease in pore size to G200 A bimodal catalyst (G200B) did not resultin an additional improvement in conversion. Thus, the pores between 100and 200 A diameter appear to be most suitable for producing high qualityliquefaction product-benzene soluble oil. This observation is similar tothe batch screening result on the optimum pore size for initialconversion. Conversion to THF solubles is not presented because they areall about 93 weight % maf for all catalysts; thermal THF solubleconversion is the same value also.

The Kaiser 100 UP unimodal alumina starts out with high conversion butrapidly declines to the thermal level in spite of its large average porediameter. However, the Kaiser alumina has a much broader poredistribution so that the pore volume in the desirable 100-200 A range issmaller than 120 A diameter catalyst, G120B, when compared on an equalvolumetric loading basis. Another factor for the rapid deactivation ofthe Kaiser-100UP may be due to the unfavorable effect of phosphoric acidused during the catalyst impregnation; the conversion is still lowerthan phosphorous containing G120BP catalyst. In addition to thesefactors, the lack of bimodality in the Kaiser alumina could also havecontributed to the rapid conversion decline. The other three catalystshave a bimodal pore distribution. The macro pores in bimodal catalystsare believed to be necessary for transporting materials into thecatalyst interior and being less susceptible to pore plugging.

For desulfurization performance, the sulfur contents of 520° C.+residfraction as well as total THF soluble liquid product are plotted in FIG.8. The resid sulfur content is more meaningful and provides a directmeasurement of desulfurization activity, since the 520° C.+residfraction is derived entirely from coal and does not contain slurry oil.The unimodal Kaiser 100 A CoMo catalyst exhibits reasonably good initialsulfur removal but the activity maintenance for resid desulfurizationrapidly deteriorates with time (similar to benzene soluble conversion)and is only slightly better than thermal after 140 hours. The referencecatalyst, HDS-1442A, shows about 0.8-0.9 weight % sulfur in resid.Increasing pore size to 120 A corresponds to higher residdesulfurization. The resid sulfur content for the larger pore 200 Acatalyst is practically the same as the 120 A catalyst. It suggests thatthe range of preferred pore sizes for resid desulfurization is somewhatbroader than that for benzene soluble conversion. Batch test resultsindicated a rather narrow pore size range around 100 A in diameter foroptimum desulfurization. However, this was based on the overalldesulfurization of total liquid product, rather than the resid fraction.

The bottom portion of FIG. 8 shows the sulfur contents of total liquidproducts which include slurry oil. The G120 A catalyst achieves thelowest sulfur level throughout the run. The other catalysts, withaverage pore size either greater or smaller than 120 A, show highersulfur contents although the differences are not large. To summarize,catalysts with relatively narrow pore size distribution around 120 Asuch as G120B are the most effective for removing sulfur not only fromresid, but also lower boiling fractions.

Table X presents other product qualities of 520° C.+resid as well astotal liquid product. The resid nitrogen contents are the same level asthe nitrogen content of maf coal; none of the catalysts seems to be veryeffective for resid denitrogenation at the test conditions used. Thereis some nitrogen removed from total liquid, and the basic nitrogencontents are approximately 56% of the total product nitrogen for thelisted catalysts. Hydrogen content of the resid increased the most withthe G120B and G200B catalysts corresponding to their good liquefactionperformance. However, a lighter product (lower specific gravity) wasproduced with G120B catalysts as compared to the larger pore G200Bcatalysts.

From the above discussions, it is evident that catalysts prepared withG120 A alumina exhibit the best overall performance for liquefaction anddesulfurization. A bimodal pore distribution having small pores in therange of 70-200 A is an important feature.

                                      TABLE X                                     __________________________________________________________________________    PRODUCT QUALITIES COBALT-                                                     MOLYBDENA CATALYSTS WITH VARYING SURFACE PROPERTIES                           Catalyst                                                                             Hours on                      Atomic                                   (CoMo) Slurry                                                                             Sp. Gr.                                                                           S N Basic N                                                                            S  N  O  N  H/C                                      __________________________________________________________________________    Thermal                                                                              --    1.116*                                                                           .44                                                                             .85                                                                             .42  1.14                                                                             1.83                                                                             4.55                                                                             5.36                                                                             .743                                     HDS-1442A                                                                            20   1.106                                                                             .19                                                                             .63                                                                             .36  .64                                                                              1.61                                                                             4.34                                                                             6.13                                                                             .843                                            121  1.110                                                                             .23                                                                             .66                                                                             .36  .84                                                                              1.70                                                                             4.23                                                                             5.84                                                                             .805                                     Kaiser-100UP                                                                         15   1.106                                                                             .21                                                                             .65                                                                             --   .71                                                                              1.69                                                                             3.88                                                                             6.07                                                                             .838                                            131  1.120                                                                             .23                                                                             .64                                                                             --   1.04                                                                             1.73                                                                             4.61                                                                             5.52                                                                             .765                                     G120B  25   1.103                                                                             .14                                                                             .57                                                                             .34  .55                                                                              1.60                                                                             3.17                                                                             6.30                                                                             .864                                            95   1.105                                                                             .20                                                                             .59                                                                             .34  .74                                                                              1.63                                                                             3.42                                                                             5.96                                                                             .818                                     G200B  27   1.108                                                                             .20                                                                             .64                                                                             --   .60                                                                              1.48                                                                             -- 6.29                                                                             .864                                            71   1.118                                                                             .23                                                                             .67                                                                             .38  .71                                                                              1.59                                                                             3.69                                                                             5.94                                                                             .817                                     __________________________________________________________________________     *At 64° C., others at 23° C.                               

What is claimed is:
 1. A supported catalyst suitable for hydroconversionof coal solids to coal liquids, said catalyst comprising a catalyticallyactive substance on support particles, said particles having essentiallybimodal pore distribution with peak concentrations of smaller poresbelow about 600 angstroms and a peak concentration of larger pores aboveabout 600 angstroms, the average diameter of the smaller pores rangingfrom about 100-200 angstroms, and the average diameter of the largerpores being in excess of 1,000 angstroms, said catalyst including atleast 5% of the total pore volume of the larger pores and at least 70%of the total pore volume of the smaller pores.
 2. The supported catalystof claim 1 including from about 7 to 20% of the total pore volume of thesmaller pores and about 80 to 93% of the total pore volume of the largerpores.
 3. The supported catalyst of claim 1 in which said catalyticallyactive substance contains molybdenum.
 4. The supported catalyst of claim1 with an average smaller pore diameter of about 120-140 angstroms. 5.The supported catalyst of claim 1 in which said support particles arecomprised of alumina.
 6. The supported catalyst of claim 1 having asurface area ranging from about 100 to 250 m² /gm.
 7. The supportedcatalyst of claim 3 in which said catalytically active substanceconsists essentially of unpromoted molybdenum.
 8. The supported catalystof claim 3 in which said catalytically active substance consistsessentially of molybdenum and a member of the group consisting ofcobalt, nickel, and mixtures thereof.